1. Field of the Invention
The present invention relates to an ink ribbon cassette and, in particular, to an ink ribbon cassette which can be suitably used in a line type thermal transfer printer.
2. Description of the Related Art
A conventional ink ribbon cassette 20 used in a line type thermal transfer printer will be described with reference to FIGS. 10 and 11. On the right-hand side as seen in the drawing, there is formed a main body portion 24 which rotatably supports a supply core 22 around which an ink ribbon 21 is wound and a take-up core 23.
Further, as shown in FIG. 11, in the vicinity of the supply core 22 of the main body portion 24, there is formed a ribbon outlet 24a through which the ink ribbon 21 wound around the supply core 22 can be drawn out in the direction of the arrow B.
Further, a ribbon guide portion 25 extends to the left from the main body portion 24. This ribbon guide portion 25 has a ribbon turn-up portion 25a in the lower portion of the forward end portion thereof and, further, there are provided a flat first ribbon slide contact surface 25b extending upwardly substantially at right angles from the ribbon turn-up portion 25a, an inclined second ribbon slide contact surface 25c connected to the first ribbon slide contact surface 25b, and a horizontal third ribbon slide contact surface 25d connected to the second ribbon slide contact surface 25c, the ink ribbon 21 being capable of being drawn around the outer peripheral surfaces of the first, second and third slide contact surfaces 25b, 25c and 25d.
The ink ribbon 21, drawn out from the ribbon outlet 24a in the direction of the arrow B, is turned up upwardly substantially at right angles (in the direction of the arrow C) at the ribbon turn-up portion 25a, and can be drawn around along the first ribbon slide contact surface 25b.
Further, between the ink ribbon 21 drawn out from the ribbon outlet 24a in the direction of the arrow B and the upper ribbon guide portion 25, there is formed a head insertion portion 26 into which a line thermal head (not shown) on the printer side can be inserted.
In the ink ribbon cassette 20 described above, by rotating the take-up core 23 in the direction of the arrow A, the ink ribbon 21 wound around the supply core 22 is drawn out from the ribbon outlet 24a in the direction of the arrow B.
And, the ink ribbon 21 is turned up by substantially 90 degrees at the ribbon turn-up portion 25a to the first ribbon slide contact surface 25b, and, from the first ribbon slide contact surface 25b, drawn around the outer peripheral surfaces of the second and third slide contact surfaces 25c and 25d in the direction of the arrow D to be taken up by the take-up core 23.
The operation of printing by a thermal transfer printer (not shown) by using this conventional ink ribbon cassette 20 will be described. When the ink ribbon cassette 20 is attached to a cassette attachment portion (not shown) on the printer side, a line thermal head (not shown) having a plurality of heat generating elements is positioned in the head insertion portion 26, and the rotation shaft of the take-up core 23 is engaged with a rotation shaft which is rotated by a motor (not shown) serving as a drive source.
Further, recording paper (not shown) is fed and positioned below the ink ribbon 21 drawn to a position below the head insertion portion 26.
Next, a platen roller (not shown) positioned below the line thermal head positioned in the head insertion portion 26 and the line thermal head are moved relative to each other to bring the platen roller and the line thermal head into press contact with each other through the intermediation of the ink ribbon 21 and the recording paper.
And, the recording paper is fed while selectively causing the heat generating elements of the line thermal head to generate heat, the take-up core 23 is rotated in the direction of the arrow A through the rotation of the motor serving as the drive source to take up the ink ribbon 21 on the take-up core 23, whereby ink of the ink ribbon 21 is transferred to the recording paper, making it possible to print a desired image on the recording paper.
In the conventional ink ribbon cassette 20 described above, the ink ribbon 21 positioned in the main body portion 24 and the ribbon guide portion 25 is exposed, so that when the operator handles the ink ribbon cassette 20, he or she may touch the ink ribbon 21 to cause it to wrinkle. When the ink ribbon 21 wrinkles, the printing quality deteriorates.
Further, at the ribbon turn-up portion 25a, the ink ribbon 21 is drawn to the first slide contact portion 25b, which is perpendicular to the ribbon turn-up portion 25a, so that the frictional resistance is maximum at the ribbon turn-up portion 25a and the first slide contact portion 25b, and the ribbon guide portion 25 is deflected to suffer deformation when the ribbon is taken up on the take-up core 23, with the result that biasing or the like occurs when running the ribbon.
Further, since the ink ribbon 21 offers large frictional resistance at the ribbon turn-up portion 25a and the first ribbon slide contact surface 25b, the take-up torque when taking up the ink ribbon 21 on the take-up core 23 is large, and a large capacity is needed for the motor serving as the drive source, resulting in an increase in the power consumption of the printer.